OP16.01: *Incidence and risk of pre‐eclampsia n twins according to gestational age, chorionicity, zygosity, and gender: a nationwide Danish study

To assess and compare the incidence and risk of pre-eclampsia (PE) in twin pregnancies, according to gestational age (GA), chorionicity, zygosity, and gender. A register-based cohort study from 2008-2018 of all dichorionic (DC) and monochorionic diamniotic (MCDA) twin pregnancies with two viable fetuses at the first trimester screening offered to all pregnant women in Denmark. We excluded pregnancies ending in miscarriage before GA 24+0, fetal reduction, and those terminated. Results were presented by descriptive statistics, and comparison was made by unadjusted time-to-event analyses at GA cut-offs before 28+0, 32+0, 34+0, 36+0, and 38+0 weeks. We included 9,398 DC and 1,947 MCDA twin pregnancies, in addition to 19,341 singletons, with no significant difference in overall PE rates among the compared groups (see table 1). However, as seen in figure 1, MCDA twins exhibited a significantly higher cumulative risk of PE at lower GAs compared to DC twins, particularly before 34+0, 36+0, and 38+0. This pattern was also observed when comparing monozygotic (MZ) to dizygotic (DZ) twins. No significant differences were noted at GA below 28+0 or 32+0. A marginal significance was observed in PE risk between male and female MZ twin pregnancies before GA 34+0, but none below or above. The risk of PE was significantly higher in MCDA versus DC twins and in MZ versus DZ twins before GA 34+0, 36+0, and 38+0, and before 34+0 between genders in MZ twins. However, there were no significant differences in the overall incidence of PE or the risk before GA 28+0 or 32+0 weeks. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.